Self propelled dynamically positioned reel pipe laying ship

ABSTRACT

A self propelled reel pipelaying ship, having forward, midship, and stern sections, and baseline, tank top, and main deck levels, comprising substantially longitudinal outer hull members and port and starboard side inner longitudinal bulkheads, each extending substantially the length of the ship, the hull members and bulkheads extending from the baseline to the main deck level in the forward and stern sections and, in the midship section, substantially above the main deck level, substantially horizontal transverse midship structural members extending between the top portions of the raised midship sections of the outer hull members and inner longitudinal bulkheads, intermediate substantially horizontal transverse members extending between the outer hull members and inner longitudinal bulkheads and vertically spaced between the tank top and midship structural members wherein the midship portions of the outer hull members and inner longitudinal bulkheads, the transverse midship structural members and the intermediate transverse members together comprise a reel support structure, and means for rotatably mounting a pipe-carrying reel to the reel support structure such that the load of the reel is distributed downwardly and outwardly, both longitudinally and transversely through the ship to maintain the stress on primary structural members of the ship within allowable stress limits for the materials used in the construction of said primary structural members.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 142,887, filed Apr. 23,1980, which in turn is a division of Serial No. 903,180, filed May 5,1978 (now U.S. Pat. No. 4,230,421, issued Oct. 28, 1980).

This application is also related to a commonly assigned application ofsimilar title filed concurrently with parent application Ser. No.903,180, by Stanley T. Uyeda et al, having Ser. No. 903,181, abandonedin favor of CIP application Ser. No. 35,216, filed May 2, 1979.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a reel pipelaying vessel. More particularly,the invention pertains to a new type of ship, specifically aself-propelled, dynamically-positionable reel pipelaying ship, in whicha pipe spooling reel and associated pipe handling equipment areintegrated into the ship's construction.

The vessel of this invention has been specifically designed toaccommodate a permanently mounted pipe spooling reel substantiallylarger than any other pipe spooling reel heretofore known or used andcapable of spooling substantially larger size pipe than any heretoforeused.

2. History of the Prior Art

In laying offshore subsea pipelines for such uses as the gathering ofoil and/or gas from offshore subsea wells, as, for example, in the Gulfof Mexico, it has been conventional to use one of two main methods tolay the pipe. In the first, or "stovepiping" method, a pipeline isfabricated on the deck of a lay barge by welding together individuallengths of pipe as the pipe is paid out from the barge. Each length ofpipe is about 40' or 80' long. Thus, the pay-out operation must beinterrupted periodically to permit new lengths of pipe to be welded tothe string. The stovepiping method requires that skilled welders andtheir relatively bulky equipment accompany the pipelaying barge crewduring the entire laying operation; all welding must be carried out onsite and often under adverse weather conditions. Further, thestovepiping method is relatively slow, with experienced crews being ableto lay only one to two miles of pipe a day. This makes the entireoperation subject to weather conditions which can cause substantialdelays and make working conditions quite harsh.

The other principal conventional method is the reel pipelayingtechnique, in this method, a pipeline is wound on the hub of a reelmounted on the deck of a lay barge. Pipe is generally spooled onto thereel at a shore base. There, short lengths of pipe can be welded underprotected and controlled conditions to form a continuous pipeline whichis spooled onto the reel. The lay barge is then towed to an offshorepipelaying location and the pipeline spooled off the reel betweencompletion points. This method has a number of advantages over thestovepiping method, among them, speed (one to two miles per hour); loweroperating costs (e.g., smaller welding crews and less welding equipmentmust be carried on the lay barge); and less weather dependency.

Historically, the technique of laying undersea fluid-carryig pipelineshad its rudimentary beginnings in England in the 1940's. In the summerof 1944, 3" nominal bore steel tubes, electrically flash-weldedtogether, were coiled around floating drums. One end of the pipe wasfixed to a terminal point; as the floating drums were towed across theEnglish Channel, the pipe was pulled off the drum. In this manner,pipeline connections were made between the fuel supply depots in Englandand distribution points on the European continent to support the alliedinvasion of Europe. (See Blair, J. S., "Operation Pluto: The Hamel SteelPipelines", Transactions of the Institute of Welding, February 1946.)

The broad concept of reel pipelaying was also disclosed in BritishPatent No. 601,103 (Ellis), issued Apr. 28, 1948, wherein it wassuggested that lengths of pipe be joined together at the manufacturingplant and coiled onto a drum, mounted on a barge or ship; the loadedbarge would then be moved to the desired marine location and the pipeunwound from the drum by fixing one end of the pipe and towing the bargeaway from the fixed location.

While the concepts described in British Patent 601,103 and thoseactually used in Operation Pluto were adequate for wartime purposes, noknown further development work or commercial use of the technique oflaying pipe offshore from reels was carried out after World War II.After a hiatus of about fifteen years, research into the reel pipelayingtechnique was renewed and was carried on by Gurtler, Hebert & Co., Inc.,of New Orleans, La.; by 1961, Gurtler, Hebert had sufficiently advancedthe reel pipelaying technique to make it a commercially acceptable andviable method of laying pipe in the offshore petroleum industry, able tocompete with the traditional stovepiping technique. The first knowncommercial pipelaying reel barge, called the U-303, was built by AquaticContractors and Engineers, Inc., a subsidiary of Gurtler, Hebert, in1961. The U-303 utilized a large vertical axis reel, permanently mountedon a barge and having horizontally oriented flanges (generally referredto in the trade as a "horizontal reel"). A combined straightener-levelwinder was employed for spooling pipe onto the reel and forstraightening pipe as it was unspooled. The U-303 first laid pipecommercially in September, 1961, in the Gulf of Mexico off the coast ofLouisiana and was used successfully during the 1960's to lay severalmillion linear feet of pipe of up to 6" diameter. The U-303 reelpipelaying barge is described in U.S. Pat. No. 3,237,438 (Tesson) andU.S. Pat. No. 3,372,461 (Tesson), both assigned to the assignee of theinvention hereof.

The successor to the U-303, currently in use in the Gulf of Mexico andknown in the trade as the "Chickasaw", also utilizes a large horizontalreel, permanently mounted to the barge such that it is not readilymovable from one carrier vessel to another. Various aspects of"Chickasaw" are described in the following U.S. Pat. Nos., all assignedto the assignee of the invention hereof:

Sugasti, et al. No. 3,630,461

Gibson No. 3,641,778

Mott, et al. No. 3,680,432

Key, et al. No. 3,712,100

Commercial reel pipelaying techniques require the use of certain pipehandling equipment in addition to the reel. Among such pipe handlingequipment essential to any commercial reel pipelaying system is astraightener mechanism. This may take the form of a series of rollers ortracks, or any other arrangement which imparts sufficient reversebending force to the pipe to remove residual curvature so that afterunspooling, the pipe will lay substantially straight on the sea bottom.No such pipe-conditioning apparatus was used in Operation Pluto orcontemplated by the British Ellis Patent.

U.S. Pat. No. 3,982,402 (Lang, et al.) describes an apparatus for layingpipe from a vertical reel in which the pipe conditioning apparatus ispivotable to adjust the lift-off angle of the pipe relative to thehorizontal (e.g., the deck of a ship) as a function of the water depthin which the pipe is being laid. This has distinct commercialadvantages, especially where the reel pipelaying system is incorporatedinto a self-propelled ship, such as that of the present invention,capable of traveling to different job sites, having different pipe sizeand/or lay depth requirements.

An early concept for a reel pipelaying ship is described in Goren, etal., "The Reel Pipelay Ship--A New Concept" Offshore TechnologyConference Proceedings, May 1975 (Paper No. OTC 2400). This paper(hereafter the Goren, et al. 1975 OTC Paper) describes advantages andoperating features of a proposed reel pipelaying ship. However, the costof construction of a ship as described there was estimated to be on theorder of $100,000,000; by contrast the ship of the herein describedinvention is currently under construction at less than one-third thatestimate. The research and development work for the ship described inthe Goren et al paper, (done at great expense by or on behalf of theassignee of this application) was subsequently materially revised innumerous major respects, and substantial changes and improvements weremade to achieve the design of the substantially different reelpipelaying ship described hereinafter; this new reel ship is or will bematerially different in concepts, construction features, mode ofoperation and results compared with the ship described in the Goren etal paper.

SUMMARY OF THE INVENTION

There is an increasing need in the offshore petroleum industry to laypipelines in deep and rough water, singly and in multiple pipelinebundles, and in remote areas far from supply bases. Thedynamically-positioned pipelaying reel ship of this invention representsa new and different approach to meeting these needs.

The fact that the reel ship of this invention is self-propelledsubstantially eliminates the need for support vessels, such as tugs andsupply boats, required by known pipelaying barges of either thestovepiping or reel laying type. In addition, the reel ship is highlymobile and has the capability of laying pipe in remote areas far fromany supply base.

The reel ship also has an advantage in being able to discharge pipe indeep water where it is extremely difficult or impossible forconventional stovepiping or reel barges to operate. This is due to theadjustable ramp assembly which mounts the pipe conditioning apparatus atthe stern of the ship; the ramp assembly is adjustable to allow pipe toenter the water at very steep angles (up to about 60°) whileconventional barges are limited to about a 15° entry angle. This allowsthe reel ship to work without a stinger, which is required byconventional barges; elimination of the stinger contributes to theability of the reel ship to work in rough weather.

A principal feature of the reel ship of this invention lies in its hullconstruction. In order to support the load of the reel and its fullcomplement of pipe, the ship utilizes a novel design which increases itslongitudinal strength, supports the reel at a height to accommodate thelargest permitted reel size, and increases the covered deck storagearea.

Another feature of the reel ship is its use of the reel hub as a ballastcompartment. In order to keep vessel roll motion to a minimum and toensure that the main propellers and thrusters are submerged sufficientlyto allow efficient and non-cavitational operation, the draft must bemaintained constant at or near the load line draft as pipe is spooledoff. To achieve this, ballast water must be added to the hull during theunspooling operation. If the water is added to the ballast tanks in thedouble bottom, the overall center of gravity of the ship (KG) is loweredwith a resulting increase in statical stability, convenientlyrepresented by GM. Increasing GM, and thus increasing ship's stability,decreases the natural period of roll and hence increases the roll motionthat will be experienced in sea conditions in which it is desirable tobe able to operate. In order to minimize this increase in GM, as pipe isunspooled from the reel, water ballast can be added to a ballastcompartment located within the reel hub in such amount as to partiallyor wholly compensate for the weight of pipe being offloaded.

For convenience, the following terms may be employed in the descriptionof this invention:

1. A "turn" is that length of pipe wound through one complete revolutionof the reel;

2. A "wrap" comprises a plurality of turns making up a layer of pipewound on the reel across the full or substantially full width of thereel.

Other features and advantages of the reel ship of this invention willbecome apparent from the following detailed description of a preferredembodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a starboard side elevation of a preferred embodiment of thereel ship;

FIG. 2 is a top plan view of the reel ship of FIG. 1;

FIG. 3 is a plan view of the main inner bottom hull structure of theembodiment of FIG. 1;

FIG. 4 is a profile of the main hull structure of the embodiment of FIG.1 with the shell plating removed;

FIG. 5 is a midship cross-section of the reel ship hull through, e.g.,frame FR 25, in FIGS. 3 and 4;

FIG. 6 is a perspective of the skeletal structure of the reel ship hullwith main deck and `tween deck plating removed between frames FR 9 andFR 49;

FIG. 7A is a starboard elevation of the pipelaying reel partly insection to show internal bracing, taken along lines A--A in FIG. 7B;

FIG. 7B is a part sectional view of the reel looking aft, through linesB--B of FIG. 7A;

FIG. 8A is a top plan view of one embodiment of the vent conduit systemof the reel ballast system;

FIG. 8B is a view along lines B--B in FIG. 8A;

FIG. 8C is a view along lines C--C in FIG. 8A;

FIG. 9A shows a sectional view of the reel shaft with its associatedpiping for a second embodiment of the reel ballast system;

FIG. 9B shows a sectional view of the venting valve arrangement mountedon the reel hub for the second embodiment of the reel ballast system;

FIG. 10A is a top plan view of the starboard reel bearing assembly andan embodiment of a starboard side reel bearing unloading mechanism;

FIG. 10B is a sectional elevation of the unloading mechanism taken alonglines B--B in FIG. 10A;

FIG. 10C is a partial section of the starboard side bearing unloadingmechanism looking forward, taken along lines C--C in FIG. 10B;

FIGS. 11A-B show plan and side views of the support ramp assemblylocated near the stern of the vessel in FIGS. 1 and 2;

FIG. 12A is a side elevation of one level wind track shown in box 12 inFIG. 11B;

FIG. 12B is a view of the starboard portion of the ramp and level windtrack looking aft, taken along line B--B in FIG. 12A;

FIG. 12C is a section of the level wind track taken along line C--C inFIG. 12B;

FIGS. 13A and 13B show top plan and starboard side elevations of thelevel wind truss assembly;

FIG. 14A is a starboard side elevation of one level wind roller carriageassembly shown in box 14 in FIG. 13B;

FIG. 14B is a view of the level wind roller carriage assembly lookingaft, taken along line B--B in FIG. 14A;

FIG. 14C is a plan view of the level wind roller carriage assembly takenalong line C--C in FIG. 14B;

FIGS. 15A-15C show plan, side, and end elevations of the level winddrive assembly;

FIG. 16 is a schematic of the skeg and props of the ship;

FIG. 17 is a graph which represents the relationship between a reelship's beam and GMT;

FIG. 18 is a perspective view looking forward of the pipe handlingequipment.

FIGS. 1-5, 7A, & B, 10A-10C, 11A, 11B, 12A-12C, 13A, 13B and 14A-14C aretaken from construction layout drawings and are drawn substantially toscale. Within each of these figures, the component parts or elements aresubstantially in proportion.

DESCRIPTION OF THE PREFERRED EMBODIMENT 1. Hull Construction (FIGS. 1-6)

The reel ship, generally designated 10, is designed to carry a mainpipe-spooling reel system and its associated support and driveassemblies, generally designated 20, and pipe conditioning equipment,generally designated 40, located aft of the reel system assemblies 20.

The ship's hull, generally designated 110, comprises a forward section112, a midship section 114, and a stern section 116. The shipconstruction is referenced primarily to frames (designated FR) whichlocate hull structural members in transverse planes. The forward section112 is defined approximately between frames FR 0 and FR 17; the midshipsection 114 which carries the reel assemblies 20, lies approximatelybetween frames FR 17 and FR 41; and the stern section 116, which mountsthe pipe conditioning equipment 40, lies approximately between frames FR41 and FR 59.

The stern section 116 preferably includes, on its underside a skeg 118which serves to increase stern buoyancy, to protect the main propellers128, such as from floating or submerged objects or from grounding inshallow water, and to provide housing for a stern thruster or thrusters122; and to improve directional stability of the vessel. The skeg, whichconsists of a substantially wedged shaped structure after part of theship's keel, is an advantageous but not essential feature of the reelship. It is particularly useful to increase stern buoyancy at relativelyshallow draft, on the order of about 13'-15', and where the size of theship may be limited by economic and/or practical considerations, such asthe need to be able to negotiate canals or ship channels of relativelylimited size.

Advantageously, the skeg is so sized that, at high draft, it contributesbetween about 1.41% and 2.1% of the ship's buoyancy; at low draft, itcontributes between about 1.04% and 1.48% of the ship's buoyancy (seeTable I below).

                  TABLE I                                                         ______________________________________                                                           SHIP BUOYANCY                                              SHIP DIMENSIONS    (as % of total ship buoyancy)                                                     High Draft Low Draft                                   Ship Length (L)                                                                         Skeg Width (W.sub.s)                                                                       (13')      (18')                                       ______________________________________                                        385'      16'          1.48       1.04                                        400'      16'          1.41       0.99                                        400'      24'          2.1        1.48                                        ______________________________________                                    

The skeg also advantageously houses one or more thruster tunnels 120 forstern thrusters 122. The bow section 112 houses one or more thrustertunnels 124 for bow thrusters 126. One embodiment contemplates the useof two bow and two stern thrusters. The bow and stern thrusters, whichare reversible, assist in course and station keeping by giving the reelship lateral or transverse positioning capability, while main props 128provide fore and aft drive and, in conjunction with the ship's rudders,positioning capability.

As an alternative to tunnel-mounted thrusters, as shown, 360° rotatableazimuthal thrusters may be utilized; such azimuthal thrusters areextendable below the hull for use and are retracted into the hull whenthe vessel is underway or entering shallow draft areas. Azimuthalthrusters would be a likely alternate when a skeg is not built into theship.

It is intended that the thrusters (whether of the tunnel or azimuthaltype) be manually controllable to allow the operator to maintain theship on a desired course, especially during a pipelaying operation. Ifthe operator determines that the ship is too far to the right or left ofthe desired course, he can apply a manual correction using thethrusters; the result is a manually controlled dynamic positioning ofthe ship. By the addition of suitable equipment, the dynamic positioningcontrol may be made automatic.

The location of the propellers with respect to the hull bottom providesadvantages in terms of efficiency of operation as well. In particular,referring to FIG. 16, the propellers must be so located with respect tothe load line to avoid cavitation; this is a function of the propdiameter (D, in feet) and the distance (H, in feet) from the mean waterline at a given ship's draft to the center of the prop. A second factorrelates to the location of the prop with respect to the hull bottom tominimize vibration; this is a function of the prop diameter (D) and thedistance (a, in feet) between the hull bottom and periphery of the prop.

It has been found that H should be 1.125 D; preferably the ratio H:D isin the range of about from 0.625:1 to 1.125:1 between vessel high andlow draft conditions, respectively. The distance "a" between the hullbottom and the tip of the propeller blades should be not less than 0.2D; "a" is preferably between about 0.2 D and 0.4 D, and most preferablyis about 0.2125 D.

FIGS. 3-6 show the primary structural arrangement of the ship. The reelpipelaying ship of this invention utilizes a novel reel supportstructure and multiple bulkhead box-beam construction in the midshipsection of the vessel to support the weight of the fully loaded reel.

American Bureau of Shipping (ABS) regulations require that primarystructural elements be continuous for the length and/or breadth and/orheight of the vessel. In the reel ship of this invention, such primarystructural elements include outer longitudinal hull walls 130(corresponding elements on the starboard and port sides are designated"S" and "P", respectively) and a double longitudinal bulkheadarrangement comprising longitudinal bulkheads 134 and 136 which lieinteriorly of a single bulkhead 132 between frames FR 17 and FR 41.

Longitudinal bulkheads 136 run substantially the length of the shipbetween frames FR 5 and FR 59. Hull walls 130 and bulkheads 134, 136extend vertically from the baseline (hull bottom) to the main deck levelexcept between frames FR 19 and FR 39 where midship portions, generallydesignated 130', 134' and 136', respectively, extend upwardly to the topof the reel support structure. Bulkheads 130', 134', and 136' taper tothe main deck level at their fore ends between frames FR 19 and FR 17and at their aft ends between frames FR 39 and FR 41.

Single bulkheads 132 which are not generally considered as primarystructural members, lie interiorly of and are spaced from the outer hullwalls 130 between frames FR 13 and FR 49 (which includes the midshipsection between frames FR 17 and FR 41). Longitudinal bulkheads 132extend vertically from the baseline to the main deck level throughouttheir length.

In the transverse direction, primary ship structural members which alsoform part of the reel support structure include web frames FR 17, FR 21,FR 25, FR 37, and FR 41. Additional fore and aft primary transversestructural members include web frames FR 5, FR 9, FR 13, FR 49, and FR59. Web frames FR 5-FR 59 extend vertically from the baseline to themain deck level of the ship. All of the transverse bulkheads, exceptthose comprising frames FR 29 and FR 33, extend across the entire beamof the ship. The bulkheads comprising web frames FR 29 and FR 33 extendtransversely only between the outer hull walls 130 and the innermostlongitudinal bulkheads 136. A space or well 152 in the midship sectionis thereby defined for receiving a pipe carrying the reel 210; this reelwell 152 is bounded by the bulkheads comprising web frames FR 25 and FR37 fore and aft, respectively and longitudinal bulkheads 136S and 136P.

In normal ship construction, the frame spacing is maintainedsubstantially equal throughout. In the reel ship of this invention, themid-section frame spacing is shortened between frames FR 25-FR 37 toaccommodate the large weight of the reel. In one embodiment, forexample, the reel weighs about 800 tons and is capable of carrying afull load of between 1,500 and 2,000 short tons of pipe.

Horizontal members of the hull structure include the baseline 138, thetank top 140, the 'tween deck 142, and the main deck 144. The tank top140 extends across the entire beam of the ship and longitudinallybetween the bow and about frame FR 52.

A pair of horizontal midship structural members 146 and 148 extendtransversely between the outer hull wall 130 and inner doublelongitudinal bulkhead 136 above the main deck 144; midship structuralmembers 146 and 148 extend longitudinally between frames FR 19 and FR39. Upper member 148 also advantageously comprises the lifeboat deck.

The main deck 144, lower and upper midship horizontal structural members146 and 148, respectively, and the portions 130', 134' 136' of outerhull wall 130 and outer and inner double longitudinal bulkheads 134 and136 respectively, between main deck 144 and upper midship horizontalstructural member 148 comprise a box-beam reel support structure,generally designated 150, which sits atop the main deck level in themidship section between web frames FR 19 and FR 39, with the endstapering to web frames FR 17 and FR 41, respectively.

The box-beam reel support structure 150 comprises a highly advantageousfeature of this invention. One of the primary problems of a reel shiprelates to the large concentrated load applied at the middle of the shipby the main reel. Substantially the entire reel load is concentrated intwo bearings, one on each side, which cover a relatively small part ofthe ship's length. If the ship is considered as being poised on two wavecrests, one at each end of the ship, the reel load concentrated on thebearings creates a large sagging or bending moment at the middle of theship which drops off rapidly in the fore and aft directions. It isnecessary to counteract this large bending moment in the center.Normally, at least a substantial part of this bending moment would becounteracted by the main deck and 'tween hull structure. However, thecontinuity of main deck 144 and 'tween deck 142 in the reel ship is lostdue to the reel well 152 located in the middle of the ship just in theregion where the bending moment counteracting forces are required. Dueto this discontinuity in the main deck and 'tween deck structure, thereis insufficient section modulus in the ship to react the bending momentcreated by the reel.

The problem of adequately reacting the bending moment due to the reelimparted load is solved in the present invention by the box-beam reelsupport structure 150. The overall structure of a vessel can beconsidered as a composite longitudinal I-beam in which the double bottomof the hull comprises the bottom flange and the main deck is the upperflange. In the reel ship of this invention, the bottom flange iscontinuous, whereas the upper flange is broken by the reel well. Theupper flange at the point of maximum bending moment has been moved up tothe top of the box section 150 and the webs are comprised of hull walls130 and double bulkheads 134, 136; the latter distribute the shear loadof the reel downwardly and outwardly in the planes of the bulkheads 134,136 to the bottom flange.

Because the bending moment due to the reel load is so peaked and dropsoff rapidly in the fore and aft directions, the box-beam supportstructure 150 need not extend more than the minimum required byclassification society (e.g., ABS) regulations. In particular, thebox-beam 150 need not extend the entire length of the ship. The lengthof the box-beam 150 (in this case the distance between frames FR 17 andFR 41) need only be at least about 0.4 L, where L is the length of theship. This is a highly advantageous feature of this invention because itreduces the amount of space required for the support system (which spaceis useable for other purposes) and reduces the overall cost of thevessel substantially.

By virtue of the fact that the support structure 150 comprises abox-beam located above and resting on the main deck level, the shearload is spread out from the reel into the structure of the ship in thefore and aft directions. The box-beam structure 150 in conjunction withthe other hull members transmit the shear load from the reel 210efficiently into the rest of the hull and ultimately into the shellplate (baseline 138) in such a way as not to exceed the load limits ofthe shell plate and so that the shear forces can be resisted by thebuoyancy forces on the shell plate.

The double bulkhead--box-beam construction used in the reel ship of thisinvention has a number of advantages, including:

1. Increasing the section modulus of the ship in the middle by the useof relatively little additional structure; the box-beam distributes thereel load through the ship so as to maintain the stress on the primarystructural members well within maximum allowable stress limits for thematerials used, according to pertinent classification societyrequirements. As a corollary, for the sagging condition the box-beam 150maintains the compressive stress in the top flange and tensile stress inthe bottom flange of the composite longitudinal beam of the vesselstructure within maximum allowable limits.

2. Supporting the rotational axis of reel 210 axis at the heightrequired to accommodate the largest permitted reel size (based onmaximum pipe diameter and length to be carried by the ship). This avoidsconstruction of a much larger ship and results in substantial costsavings.

3. Providing a longitudinal passageway between bulkheads 134 and 136 foraccess to compartments such as storage and/or personnel cabins locatedbetween the bulkheads 134 and bulkheads 132.

4. Creating additional enclosed spaces for winches and other equipment,including, for example, the diving equipment. This additional space wasmade available by the discovery that it was not necessary to extendbulkhead 132 vertically to the full height of the box-beam structure150. Rather, it was discovered that by advantageously havinglongitudinal bulkheads 134, 136 span the reel bearing support blocks(described below), substantially all of the effective load istransmitted through bulkheads 134, 136 to the lower composite beamflange (i.e., the double bottom of the ship's hull). Thus, a verticalextension of bulkhead 132 became superfluous.

In addition to the above-discussed advantageous features of theconstruction of the reel ship, other new and desirable features, asfollows, are also apparent and are useable in preferred embodiments.

One of the advantageous features of the reel ship is its ability tooperate in relatively shallow draft areas. The ship is designed to drawas little as 13'-14' of water, thereby enabling it to operate inessentially unlimited areas, including such as Australian waters, wheresand bars limit vessel drafts to about 13 feet. Equally, or moreimportant, the reel ship can operate out of shallow water ports, such asassignee's reel pipelaying shore base at Houma, La. Generally, a reelshore base requires a fairly large expanse of dock area. The land atdeepwater ports is generally at a premium; shallow water port land ismuch less costly. Thus, there are economic and commercial advantages toa ship which can operate out of a shallow water base.

As a consequence of its shallow draft capability, provision must also bemade for ballasting the ship down to its operating draft. This isadvantageously accomplished by the double bottom hull design, in whichthe tank top 140 is spaced about twice the normal distance from thebaseline 138 (normal spacing is about 3.5'; whereas in a preferredembodiment of this ship, the spacing is on the order of 7'). Space isthereby created for sufficient ballast to sink the ship to its desirednormal operating draft (e.g., about 18 feet).

The space between bulkheads 132 and outer hull members 130 is void sothat the construction of the major part of the vessel is equivalent to adouble hull arrangement, at least between frames FR 13 and FR 49. Thisprovides good reserve damage stability to the ship.

1a. Vessel Characteristics

An important hydrostatic characteristic of the reel ship that affectsits hydrodynamic characteristics (i.e., that has an effect on its motionin waves) is its GMT (i.e., the vertical distance (in feet) from itscenter of gravity to the transverse metacenter of the ship). GMT changeswith changes in the vessel load; generally GMT increases as the shipbecomes lighter, i.e., as vessel load and draft decrease.

If the GMT of the vessel is too small, the vessel becomes staticallyunstable; slight shifts in weight, e.g., as the booms of cranes mountedon the vessel are swung around, will cause the vessel to heel asubstantial and highly undesirable amount, possibly up to 10°. On theother hand, if the GMT of the vessel is too large, the ship becomes toostiff and the roll will be too great for acceptable operating conditionsfor personnel and equipment in prevailing seas.

In the reel ship of this invention, over 2,000 tons of pipe may beoffloaded during a laying operation. As pipe is payed out from the ship,and the ship becomes lighter, the GMT will increase. If no adequatecompensation is made for the removed pipe weight, the GMT could increaseto the point where the pipelaying operation may have to be terminatedprematurely because of excessive rolling action of the ship. In otherwords, without appropriate compensation, the reel ship would be limitedto a more restricted range of operating sea conditions.

For example, consider vessel displacement at full load to be about13,000 tons with an operating draft of about 18 feet. If no ballast isadded after offloading the pipe, the vessel displacement will be around11,000 tons and the draft will be 15 feet, resulting in the vessel beingraised 3 feet out of the water. The GMT of the vessel changes from about5.5 feet to about 13.3 feet, an increase of about 7.8 feet. (See TableII below, which compares the approximate GMT of the vessel under fullload, half load and empty reel conditions, where no reel ballast isadded and where ballast is added to the reel hub (or core) as pipe isunspooled.) This increases roll stability of the vessel so that the shipbecomes stiffer about the roll axis and increases the rate of roll ofthe vessel. Equally, if not more importantly, such decrease in draftreduces the efficiency of the main props and thrusters and increases thecavitation problem, as noted above.

The change in GMT of the vessel, from about 5 feet to nearly 14 feet asthe pipe weight goes from 2,000 tons to 0 tons, would be a large changefor a vessel of this type and size. In practical effect, this would bedetrimental to the safety and comfort of personnel, to on-deckequipment, to overall ship operations, to the pipelaying operation inparticular, and to the reel itself (due to excessive loading of thebearings and other reel support elements).

In order to maintain relatively constant displacement of the ship aspipe is payed out, ballast can be added in a conventional manner to hullballast tanks (e.g., between the baseline and tank top). Although suchbottom ballast will keep the draft at about 18 feet, the center ofgravity of the vessel will shift downwardly as ballast is added. Theresult will be a change in GMT which may be outside acceptablecommercial operating limits for the safety of personnel and equipment inprevailing seas.

In order to maintain commercially acceptable motion characteristics, itis a requirement that the GMT of this vessel be maintained within 25% ofits initial height, which for commercial purposes, should not be morethan about 7 feet, although a change of between 25% and 30% can betolerated during the unreeling operation, and a greater changetoleranted in calm sea conditions. Once a nominally optimum GMT for thevessel is determined, it is then desirable to maintain the change inthis GMT as small as possible and at least within acceptable limits toavoid the overstability and excessive motion problems noted above.

For sea conditions in which normally expected maximum wave periods arein the range of about 5-8 seconds, the GMT (in feet) of such a reel shipshould be no greater than 0.00194B², where B is the beam (in feet) ofthe vessel. FIG. 17 shows the relationship between GMT and beam B for anatural vessel period T_(n) of 10.0 sec., a commercially advantageousminimum period. The shaded area under the curve represents maximumcommercially acceptable values of GMT for a reel ship of this invention.Advantageously and preferably, the GMT of the reel ship should bebetween about 3 feet and 8 feet under all significant offshore operatingconditions. In order to maintain this GMT range, it has been foundhighly advantageous and preferable to provide ballast compensation atthe level of the reel, and particularly in the reel hub, as pipe isunspooled (see Table II below).

                  TABLE II                                                        ______________________________________                                                     CMT (in feet)                                                                   without   with core                                            Reel Load      core ballast                                                                            ballast                                              ______________________________________                                        Full            5.51     5.51                                                 one-half       10.22     6.68                                                 empty          13.26     7.60                                                 ______________________________________                                    

It is desirable that the hub be sufficiently large to accommodate enoughballast to maintain the change in GMT within commercially acceptablelimits. In one preferred embodiment, the reel has a capacity to spool upto about 2,000 tons of pipe; the hub can hold up to about 1,600 tons ofballast. The remaining necessary ballast can be added to conventionalhull tanks without adversely increasing the change in GMT of the ship.

In addition to the above-mentioned advantage of minimizing the change inGMT as the pipe is offloaded during a lay operation, the use of reel orcore ballast has other advantages to the ship to this invention. Forexample, if the ship is carrying out a partial load of pipe, ballast canbe added to or removed from the reel core to change the natural rollperiod of the ship and thereby reduce its roll motion. In this way, theGMT of the ship can be changed to adjust for varying sea conditions; inparticular, the natural roll period of the ship can be changed, asnecessary, with respect to prevailing wave periods to prevent resonanceconditions from occurring.

The reel ship, with no reel load but with sufficient bottom ballast toachieve its operating draft of about 18 feet, has a very high GMT (witha concomitant short natural period). This results in a tendency of theship to whip with high acceleration and deceleration forces. By addingballast to the reel core, the GMT of the ship can be decreased to detunethe vessel and create longer, slower roll periods, i.e., the naturalperiod of the ship is increased.

Additionally or alternatively, the vessel roll may be damped by the useof bilge keels 156 and/or flume tanks (not shown). The bilge keels 156are provided along the parallel mid-body of the vessel on the turn ofthe bilge as an aid in cutting down on ship's roll; preferably thesekeels should not extend beyond the outer projected horizontal andvertical vessel surfaces at least in part as protection against breakingoff.

With respect to other vessel characteristics, it has been found that thelength of the ship should be preferably between about 385' and 410°; thebeam is preferably between about 60' and 80' and more preferably betweenabout 68' and 73'. The ratio of beam (B) to draft (D) is preferably inthe range of about 2.25:1-4.00:1 and more preferably in the range of3.5:1-4.0:1.

2. Reel Assembly (FIGS. 7-10)

The pipe spooling reel system 20 comprises a reel 210 located near thelongitudinal center of buoyancy, which is near the longitudinalgeometric center of the vessel.

Reel 210 (see FIGS. 7A-B) is comprised of a central axis shaft, generalydesignated 212. Axially opposite flanges, generally designated 214S,214P, extend radially outwardly from shaft 212. A hub, generallydesignated 216, co-axial with shaft 212, extends between flanges 214Sand 214P. Each flange 214 is composed of a plurality of radial arms 218extending from the shaft 212 outwardly to the flange rim. Typically,radial arms 218 may be spaced 30° apart around the circumference of theshaft 212. A further plurality of shortened radial reel arms 220, whichextend radially outwardly from the surface of hub 216 to the flange rim,are located between adjacent arms 218.

The reel hub 216 comprises a circumferentially and axially continuousouter surface covering 222 extending between flanges 214S and 214P. Aplurality of annular spacers 224 extend from the interior face of hubsurface covering 216. The other ends of annular spacers 224 are secured(e.g., by welding) to transverse bracing members 226 which extendbetween opposed flanges 214S and 214P. Web plates 228 lie in radialplanes between the interior surface of hub covering 216 and transversebracing members 226 and between adjacent annular members 224. Thisinterior construction of the reel results in a criss-cross or honeycombstructure under the plating 222 of hub 216. Such construction produces areel with great strength necessary to accommodate large back tensionforces which may occur during pipe laying and/or pipe retrievaloperations. Such back tension forces produce a wedging action betweenadjacent turns of pipe in a wrap which cause large splitting forces todevelope in the reel flanges 214.

Advantageously and preferably the ratio of the diameter of the reel (atthe flange rim) to the width of the reel hubs for the reel ship is inthe range of between about 3:1 and 4:1; more preferably, this ratio isin the range of about 3.5:1-3.8:1; still more preferably such ratio isabout 3.7:1. In the preferred embodiment designed for construction, thereel diameter is about 82 feet and the hub width is about 22 feet.

2. Reel Ballast System

An important and advantageous feature of this invention lies in the factthat the interior of the hub 216 comprises a water-tight compartment towhich ballast may be added as pipe is spooled off the reel. This ballastsystem requires means for supplying ballast, advantageously sea water,to the reel hub while the reel is rotating, at the same time providingmeans for venting the hub.

A first embodiment of such a ballast system is shown in FIGS. 7A-7B. Inthis embodiment, shaft 212 comprises machined end portions 230, eachhaving a central axial bore 232. End portions 230 extend from a tubularcentral portion 234 which has support plates 236 spaced from each otheron the inside of tubular portion 234. Shaft ends 230 and tubular centralportion 234 together act as unitary shaft element 212.

A fill and drain conduit 238 extends axially into the reel through oneaxial shaft bore 232 (e.g., bore 232P); inside the reel, conduit 238makes a 90° bend and extends radially outwardly toward the interiorsurface of hub 216. The end portion of conduit 238 may be secured to atransverse member 226. A second or vent conduit 240 extends axially intothe reel through the other shaft bore (e.g., bore 232S). Inside thereel, conduit 240 makes a 90° bend and extends radially outwardly towardthe inner surface of hub 216; the end portion of conduit 240 may besecured to a transverse bracing member 226. Advantageously andpreferably, conduits 238 and 240 extend in opposite radial directionsfrom each other.

In one relatively simple embodiment, the fill and drain conduit 238 maybe connected through a swivel connection to a T conduit, connected inturn through valve means to a pump which pumps ballast into the reel andto a drain conduit which pipes ballast overboard. Closing the outletvalve and opening the inlet valve permits sea water ballast to besupplied to the interior of the hub 216; opening the drain valve andclosing the inlet valve allows the ballast to drain out of the hub andoverboard.

Referring now to FIGS. 8A-8C, vent conduit 240 may be connected througha conduit 242, having an exterior cammed surface 246, to a swivelconnection 244. The other side of swivel 244 is connected throughconduit means to a vent discharge. The arm of a switch mechanism 248contacts cammed surface 246 on conduit 242 to control the opening andclosing of valves in the vent discharge line. The switch mechanism 248is adjusted so that the valves are open for only a short period of time,e.g., when the opening of vent conduit 240 is within plus or minus 30°of its apex of rotation. This arrangement prevents a discharge ofballast water when the vent pipe rotates a sufficient distance to besubmerged within the hub.

In an alternate arrangement, shown in FIGS. 9A-9B, tubular section 262between shaft end 230 and a sealing plate 264 contains a number ofopenings 266 which communicate the interior of the tubular shaft portion262 and the reel hub interior. The outer end of shaft portion 230 may besealed by a flange 268 through which a pipe 270 extends. The outer endof pipe 270 may be connected through a swivel joint 272 and a gate valve274 to a fluid supply conduit 276. A spring-loaded pressure relief valve278 may be provided to avoid excessive fluid pressures from building up.

During the course of a pipelaying operation using this alternatearrangement, as the pipe is unspooled from the reel, water ballast ispumped into the reel hub through the valve 274, swivel joint 272,conduit 270, and openings 266 is shaft portion 262. As water is pumpedin, air in the hub is vented to the outside through venting valves,generally designated 280 (FIG. 9B). At least two such venting valves areprovided approximately 180° apart on one or both of flanges 214. Ventvalves 280 comprise a gravity-operated scupper valve 282 and alever-operated butterfly valve 284. The disc 282a of the scrupper valveis grvity operated. Thus, as the reel rotates and the valve travelsdownwardly, at a certain point the disc 282a will be pulled closed,aided, if necessary, by the pressure of the ballast water in the hub asthe valve moves below the water line; the escape of water ballast fromthe reel is thereby prevented (other than a possibly minimal amountwhich may escape before the valve is fully closed). As the reelcontinues to rotate and vent valve 280 moves up, it will eventuallyreach a point where the scupper valve 282 is above the water line andgravity pulls disc 282a down. This opens the vent valve 280 to vent airout of the reel hub interior. The butterfly valve 284 is normally keptopen and is used essentially as a manual closure.

2b. Reel Support System (FIGS. 10A-10C)

The reel shaft 212 seats in a pair of axially opposite bearings 290. Thebearings 290 can be any commercially available shelf bearings (e.g., FAGModel No. 539948 roller bearing). The bearings 290 rest on bearingsupport blocks 292. Bearing support blocks 292 in turn are secured tothe upper midship horizontal structural members 148 comprising the topof the reel support structure 150. As noted earlier, the bearing blocksrest on bulkheads 134, 136, which distribute the reel and bearing loaddownwardly and longitudinally outwardly through the reel supportstructure 150 to the baseline 138.

Preferably and advantageously, the reel may be horizontally locatedwithin about ±5% of the longitudinal center of buoyancy. In thepreferred embodiment of the vessel as designed for construction, theship has a length of between about 385'-410'; the reel may be locatedwithin a range of about 20' fore and aft of the longitudinal geometriccenter.

When at sea, the reel ship will sometimes encounter heavy sea conditionswhich cause the vessel to roll from side to side, thereby placing largeloads on the beaings. It may therefore be desirable to unload thebearings when the ship is traveling between pipelaying operations,particularly if smaller beaings than those presently contemplated areused or if the reel size and capacity are increased relative to thebearing size. For this purpose, means may be provided for unloading thebearings, preferably by jacking up the reel shaft to raise it off thebearing seat. An added advantage of this bearing unloading capability isthat the bearings can be repaired or removed while the vessel is at sea.

One such unloading mechanism which could, if desired, be incorporatedinto the reel ship is shown in FIGS. 10A-10C. In this embodiment, aportion 154 of the reel well bulkheads are recessed between frame FR 27and FR 35. This recess provides space for mounting a reel shaft supportmechanism, generally designated 300. The support mechanism 300 includesa support truss 302, having wedge-shaped bottom portions 304, 306,between which is a generally flat bottom section 308. The upper face ofthe support truss 302 contains an arcuate recess 310. A pair of gussets312, having arcuately shaped inner faces co-radial with the arc ofsurface 310, are located on the upper face of support trust 302 tocontinue the arc of surface of 310. An arcuate plate 314 is secured atits ends to gussets 312 and completes the circle which surrounds shaft212. One or more hydraulic cylinders 316 mounted on the recessed deckportion 154 engage the bottom surface portion 308 of support truss 302.In the preferred embodiment, up to four hydraulic cylinders, each havinga 400-ton lifting capacity, are employed with each of the port andstarboard side reel shaft support mechanisms 300. A pair oflongitudinally opposed movable end wedges 318a, 318b rest on therecessed deck portion 154 and are slideable under wedge-shaped bottomportions 304, 306 of truss member 302. Wedge members 318 are driven byrespective hydraulic jacking screws 320a, 320b. Wedges 318 co-operatewith hydraulic cylinders 316 to lift the support truss 302 and shaft212, and to retain the truss 302 and shaft 212 in their elevatedpositions. By this arrangement, a strong adjustable structural supportis provided for the shaft 212 and reel 210 which allows the bearings 290to be unloaded for extended periods, such as under heavy sea conditionswhen the ship is traveling between jobs, or when bearing repair isrequired.

2c Reel Drive System

The reel drive system includes a drive gear 330 mounted around the outerrim of one or both flanges 214. In the embodiment shown, the drive gearis located on and circumferentially around the rim of starboard flange214S. The reel is driven by one or more motors, as shown, for example,in the aforementioned Lang, et al. patent and/or Goren, et al. 1975 OTCpaper. 332. Such motors are advantageously hydraulic motors (e.g.,Hagglund Hydraulic Motor Model #H8385 with Brake Model #FBC-80-2-D orequivalent). The invention is not limited to the use of hydraulic drivemotors; D.C. motors are also suitable because of their high torquecapability at low speed. The reel drive mechanism also incorporates anautomatic tension control feature which maintains a relatively constanttension on the pipe, particularly during lay and/or retrievaloperations.

3. Pipe Conditioning Equipment (FIGS. 11-15)

The pipe conditioning equipment, generally designated 40, is mountedsternward of the reel assembly 20. The pipe conditioning equipment 40includes, inter alia, a main support ramp assembly 410 and a level windassembly 450. The level wind assembly 450 has various pipe handlingequipment mounted thereon, including a pipe bending radius controller490, pipe straightening equipment 510, a tensioning assembly 520, a pipeclamp assembly 530, a stern pipe guide assembly 540, and various fixedand/or movable work platforms.

3a. Support Ramp Assembly (FIGS. 11-12)

The support ramp assembly 410 preferably comprises an open trussframework of a type shown, for example, in FIGS. 11A-11B. The rampsupport assembly 410 comprises upper and lower longitudinal framemembers 412 and 414, respectively. These longitudinal frame members areadvantageously interconnected by vertical, horizontal and/or diagonalbracing members for additional strength. Upper frame members 412 arelonger than lower frame members 414; the upper and lower frame membersare longitudinally offset from each other and are connected at theirforward end by structural members 416 and at their aft end by structuralmembers 418.

The support ramp assembly 410 mounts a plurality of tracks 420 extendingtransversely across the support ramp assembly. Tracks 420a-420d aremounted on upper frame members 412 so as to be substantially co-planerwith each other. Track 420e is located on connecting member 416 at anangle relative to the plane of tracks 420a-420d.

FIGS. 12A-C show details of a typical ramp mounted level wind track 420.A track base support member 422 extends approximately orthogonally fromeach of upper frame members 412S and 412P. A track base plate 424extends between and is secured (e.g., by welding) to each of track basesupport members 422. A T-shaped track member 426 having flared ends 428extends upwardly from track base plate 424 and transversely betweenupper ramp frame members 412. The axially opposite ends of track members426 are secured (e.g., by welding) to end support plates 430 which, inturn, are secured to the upper frame members 412 and track base supportmembers 422. Additional intermediate track support members 432 may beprovided to give the track 426 additional strength.

The support assembly 410 is mounted to the stern portion of the vesselat pivot points 411. Advantageously, a jacking truss 550 may bepivotably connected at one end to the support ramp assembly 410 and atthe other end to a jacking mechanism 552 mounted on tracks 554 securedto the vessel deck. The jacking mechanism may be moveable along thetracks to pivot the ramp support assembly 410 about pivot points 411.This allows adjustment of the pipe path through the pipe handlingassemblies to thereby adjust the exit or lay angle of the pipe relativeto the water.

3b. Level Wind Assembly (FIGS. 13, 14)

The level winder 450 consists of a main frame 452. A level wind framesection 454 extends from the forward end of main level wind frame 452and at an angle thereto which essentially follows the angle of rampframe connecting member 416.

A plurality of level wind roller carriages 456 extend from the undersideof level wind truss 452. The basic construction of each carriage 456 isthe same and comprises downwardly extending fore and aft carriagemembers 458 connected at the top by transverse frames 460 and at thebottom by transverse frame 462. The carriage is located so that atransverse frame member 464, comprising part of the level wind truss,lies intermediate transverse carriage frame members 460a, 460b. Each ofcarriage members 460 mounts a roller 466 (e.g., Hilman Roller Model No.5XTDW 200-ton capacity) which rides on a corresponding flared end 428 ofT-shaped track member 426. A third or top roller 468 (e.g., HilmanRoller Model No. 6X 300 ton capacity) is mounted to transverse framemember 464 and rides on the flat top surface of T-shaped track member426. An optional fourth or bottom roller 470 (similar to rollers 466) isprovided, especially on carriages 456c and 456d; bottom roller 470 ismounted to bottom frame member 462 and co-operates with the track baseplate 424.

It will be seen that the level wind roller carriages 456 essentiallysurround the level wind tracks 420 while permitting the level windstructure 450 to traverse the width of the support ramp 410.

The level wind drive system may employ, in one contemplated embodiment,a hydraulic motor 472 connected through a chain drive to a drive shaft474 which is mounted through bearing supports 476 to one of the rampsupport frame members 412. Bevel gears 478 connect the drive shaft 474with a plurality of jack screws 480 which extend transversely across theramp assembly 410 between frame members 412S and 412P. The externallythreaded jack screws 480 are threaded through complementary threadedopenings in downwardly extending level wind drive connecting members482. The hydraulic motor 472 rotates the drive shaft 474 which, throughbeveled gears 478, rotates jack screws 480. Such rotation of the jackscrews 480 produces a traversing motion of the level wind assembly 450across the width of the ramp support structure 410.

3c. Pipe Bending Radius Controller

At its forward end, the level wind assembly 450 mounts a stressuniformizer or pipe bending radius controller 490. The radius controllerassembly may comprise a plurality of rollers 492 mounted to curved framemembers 494, which are secured to the level winder frame 452. The radiuscontroller is connected to the level winder through pivot mountingassemblies 496. A jacking mechanism 498 (e.g. a hydraulic screw jack) isadvantageously coupled between the level wind forward frame members 454and the radius controller frame 494. Through operation of the jackingmechanism 498, the radius controller can be pivoted about pivot mounts496 as needed to adjust for the size of pipe and support ramp angle. Inthis manner, the amount of curvature to be imparted to the pipe beforeit enters the straightener 510 can be properly established for varyingoperating conditions.

The radius of curvature of radius controller assembly 490 isadvantageously and preferably approximately the same as the minimumradius or curvature to which the inner wrap of the largest diameter pipecapable of being spooled on the reel 210 can be bent. The radiuscontroller 490 imparts a substantially uniform stress and substantiallyconstant radius of curvature to pipe as it is unspooled and prior to itsentry into the straightener apparatus 510. The ratio of the radius ofthe reel hub R_(H) to the radius of the radius controller R_(RC) lies inthe range of between about 1.2:1.0 and 1:1.2; more particularly, theprefered ratio is about 1.0:1.0.

3d. Straightener Assembly

A straightener assembly 510 is mounted to the level wind assembly 450downstream of the radius controller assembly 490 (in the direction ofpipe unspooling). The purpose of the straightener assembly 510 is toimpart a reverse bending force to the pipe sufficient to overcome thecurvature set by the radius controller 490. For this purpose, threereaction points are required to be exerted on the pipe, the two endpoints acting in one direction and the intermediate point acting in theopposite direction, such that all 3 forces are substantially coalignedin the plane of pipe bending. A two-roll straightener can be used inwhich the radius controller is considered as one reaction point.Advantageously and for greater flexibility of operation, a "three-roll"straightener apparatus 510 is used; the straightener rolls may, in fact,comprise tracks of the type described for example in assignee's U.S.Pat. No. 3,680,342, the entire disclosure of which is incorporated hereby reference.

Advantageously in the preferred embodiment designed for construction,the straightener assembly 510 comprises a first track assembly 512 asecond track assembly 514 and a third track assembly 516. Forconvenience hereafter the straightener track assemblies 512, 514, 516will be referred to generically as "straightener rolls", it beingimplicit therein that the track assemblies can be replaced by individualrollers, if desired.

The first straightener roll 512 is mounted to and between radiuscontroller frame members 494 and is pivotably movable therewith ascontrolled by jacking assembly 498. Straightener roll 514 is mounted ina straightener frame assembly 518 carried by the level wind 450.Straightener roll 514 is located on the opposite side of the pipepassage from straightener roll 512 and is adjustable in a directionsubstantially perpendicular to the nominal longitudinal axis of pipepassing through the pipe conditioning apparatus 40. The thirdstraightener roll 516 is also mounted in the straightener frame 518 onthe same side of the pipe passage as the first straightener roll 512;straightener roll 516 is substantially fixed in position.

One of the features of the three roll straightener apparatus of thisinvention is that both of the first and second straightener rolls 512and 514, respectively, are adjustable relative to each other and to thenominal pipe passage to thereby maintain the actual pipe path as closeto the desired nominal as possible for varying pipe sizes and rampangles.

The straightener assembly also incorporates the tensioner apparatus 520.Specifically, in the presently preferred embodiment, the tensioner maycomprise a track or roll 522 mounted in the straightener frame 518 andadjustable in a direction substantially perpendicular to the nominalpipe path in a similar manner as straightener roll 514. Once suchsuitable tensioner mechanism is used on the aforementioned "Chickasaw"and is described in one or more of the above referenced Sugasti et al,Gibson, Mott et al and Key et al U.S. patents, the entire disclosures ofwhich are incorporated here by reference.

3e. Additional Equipment

Additional pipe handling equipment, including a movable clampingassembly (not shown), a fixed clamping assembly 530 and a stern pipeguide assembly 540 are also located on the level winder assembly 450.This additional pipe handling equipment is not germane to the presentinvention and no further details thereof are described herein.

The pipe coming off the reel 210 should make sufficient contact with theradius controller 490 at a tangent thereto to bend the pipe sufficientlyso that each wrap of pipe being unspooled will have the same amount ofcurvature as it enters the straightener.

One way which has been suggested to accomplish this uniformity would beto pass the pipe through a preferably vertically adjustable set ofrollers 562 located on a tower 560 aft of the reel 210. The rollers 562force each wrap of pipe to have a sufficiently large radius of curvatureto be tangent to the radius controller 490 as the pipe is unspooled.Absent rollers 562 or some similar mechanism for imparting the desiredbending moment to the pipe, each wrap of pipe unspooled would have adifferent set; that is, the inner wraps have a smaller radius ofcurvature than the outer wraps so that the curve on the free pipebetween the reel and the pipe conditioning equipment would change as afunction of the wrap being unspooled; this, in turn, would cause thepipe to contact the radius controller at a different location for eachwrap, thereby altering the effect of the radius controller and itsability to impart a uniform radius of curvature to the pipe before itpasses through the straightening assembly 510.

As an alternative to the tower shown, it is considered that a "freefloating" roller assembly may be used. Such roller assembly would rideon the upper surface of the pipe and be tied to the deck of the ship bycable, thus, the pipe and cables together act as the roller support,with the pipe exerting an upward force and the cable a downward force onthe rollers.

The roller assembly 562 whether tower-mounted or cable tethered,increases the ability of the reel to impart larger hold-back tensions onthe pipe than would be possible without such roller assembly 562. Thisfactor increases the capability of the ship of this invention to laylarger pipe in deeper water than might otherwise be the case.

4. Portable Reels

The reel ship of this invention is capable of carrying spooled pipe on"portable" reels, that is, reels which do not form part of the basicship construction, but which are mounted on, e.g., skids, and may beoffloaded at the shore base. This advantageous feature permits the shorebase to prespool pipe on such portable reels and store the spooled reelsin the yard while the reel ship is at sea. When the ship returns toport, any empty portable reels on board can be removed and theprespooled waiting reels be loaded on board, thereby reducing down timein port.

Advantageously, one or more such portable reels, generally capable ofcarrying up to 6" diameter pipe, may be mounted on the clear deck spaceforward of the main reel 210. This secondary pipe may be passed over themain reel to the pipe handling apparatus 40. The secondary pipe maybypass the straightener assembly 510 and be bundled with the main pipeupstream of the stern guide assembly 540 so that it enters the water atthe same lay angle as the main pipe.

5. General Characteristics

In a preferred embodiment of this invention, the reel 210 has a diameterof about 82 feet. Pipe capacity is about 2,000 tons. Capacities in termsof pipe size and length are shown below:

    ______________________________________                                        Nominal Pipe Size                                                                              Approximate Capacity                                         (Inches)         (Feet)    (Miles)                                            ______________________________________                                        4                267,000   50.5                                               6                160,000   30.2                                               8                104,000   19.7                                               10               73,000    13.8                                               12               54,000    10.3                                               14               45,000    8.5                                                16               30,000    5.7                                                ______________________________________                                    

Capacities shown are for typical projects in medium to deep water. Thevessel is also capable of carrying two portable reels with totalcapacity of 500 tons. The portable reels are positioned so their pipesmay be payed out as a bundle with the primary pipe.

Other characteristics of the preferred embodiment of the reel ship ofthis invention are (approximately):

    ______________________________________                                        Length overall     405 feet                                                   Beam                70 feet                                                   Depth               28 feet, 6 inches                                         Draft, operating    18 feet                                                   ______________________________________                                    

6. Applications

Below are discussed a number of uses for the reel ship in the offshoreconstruction industry.

6a. Subsea Completions

Of the many potential uses employed by the reel ship, one of the mostimportant applications is in subsea completions and subsea tie-ins.Major advantages include:

1. Pipe is welded and tested on shore before laying offshore. This isespecially an advantage for through flow lines; which can be driftedbefore laying.

2. Speed of laying pipes offshore substantially reduces delays due toweather and minimizes interference with field operations.

3. Since the vessel can dynamically position itself next to platforms,wellheads, etc., the danger to underwater pipelines or other bottomequipment is minimized. The reel ship is also much faster in setting up,moving away from, and moving between locations.

4. Except on the largest of projects, one load of pipe is all that isrequired to complete pipelines to subsea wellheads.

5. The reel ship can lay bundled configurations made up of pipes orcombinations of pipe and cable as desired.

6b. Bundled Pipelines

In the "stovepiping" method of laying pipeline offshore, a new sectionof pipe must be welded (added) every 40 or 80 feet. This method requiresone "welding line" for one pipeline. If it is desired to lay pipe inbundles, then, in effect, a "welding line" must be set up for each pipein the bundle. Since most standard pipelay barges are designed for justone pipeline, finding enough room for one or more additional pipe"welding lines" is difficult.

Furthermore, most pipeline vessels apply tension to the pipe with theuse of a tensioner, specifically designed to handle one pipe, and nottwo or more.

These problems are overcome by the reel ship of this invention with theuse of the main reel and one or more portable reels. A typical bundle,for example, could consist of an eight inch pipe coming off the mainreel and four inch and two inch pipe coming off separate portable reels.It is also possible to have more than one pipe bundled together on areel.

Pipes for different lay operations can be carried together on the reels.The experience of the assignee and/or its predecessors-in-interest inlaying pipe by the reel method has shown that different size pipes canbe spooled over other pipes without damage.

Because of the large spooling capacity of the reel ship of thisinvention on the main and portable reels, pipe can be carried on onetrip for a number of separate lay operations, such as those required ona subsea completion project.

6c. Operation in Congested Areas

In an area which is congested with many platforms, pipelines, subseacompletions, construction barges, supply boats, etc., the vessel whichcan operate without the use of a conventional anchoring system will havea great advantage.

One example of this application would be in a developed field whichalready has many operating pipelines. If the need arose to bring anadjacent field's production into this facility by pipeline, it could beeffectively accomplished with the dynamically positioned reel ship. Withthe pipe already loaded onto the reel, the ship would dynamicallyposition itself next to the platform in the developed field, feed outthe end of the pipe to the platform and lay away from the structure,thus requiring only a minimum time in the congested area.

Another application of the dynamic positioning capabilities of the reelship would be pipeline tie-ins at platforms, subsea completions ormanifold centers. Besides the reduced risk by not using anchors, thespeed at which the ship can set up on location, move between locations,and move off location at the end of the job, will allow the maximum timeto be devoted to completing the project during favorable weatherperiods.

6d. Laying Pipe in Shipping Lanes

Modern pipeline barges can lay more than two miles of pipe in a 24-hourperiod by the "stovepiping" method; present-day reel barges can lay thesame amount of pipe in a fraction of that time. In each case, the bargeanchor patterns in doing this may cover an area approximately threemiles long and one mile wide. If this area is located in a majorshipping land, such as the English Channel, unnecessary delays toshipping could be expected.

In contrast, the reel ship could lay the two miles in a few hours, and,since no anchoring pattern is used, the vessel would occupy only anominal width of the shipping lane during any particular period of time.The reel ship's unique pipelaying operation offers a means of reducinginconvenience to shipping when pipelines must be installed in areas withheavy commercial shipping traffic.

6e. Remote Locations--Worldwide Operations

Certain areas of the world, such as the Beaufort Sea, allow very littletime each year for offshore construction. Similarly, land support basesand the logistics associated with the base operations, offer difficultyin supporting offshore operations.

The reel operation of the reel ship offers advantages, of which a feware listed below:

The speed at which the reel ship can travel to such locations.

The large pipe capacity the reel ship can carry in one trip.

The speed in laying offshore.

Minimum shore support if complete requirement of pipe can be carried inone load.

The reel ship will be able to mobilize from the Gulf of Mexico tooffshore areas such as the North Sea, California, Brazil, and theMediterranean in approximately 21/2 weeks; the North Sea to theMediterranean will take only one week.

Since the reel ship has a large carrying capacity for smaller pipes, itwill be able to operate from a base, for example, in the North Sea, andmobilize to an area like the Mediterranean. This eliminates the need toset up bases in every area where pipe is laid.

In short, the reel ship is able to mobilize, complete the job, anddemobilize in a short period of time.

7. Operating Example

The following example is presented to illustrate the basic reel methodlaying procedure.

A. Pipe size--10-inch nominal

B. Pipeline length--25 miles

The basic operation begins with coated pipe delivered to the spoolingyeard. The pipe is welded into approximately 1,700 foot lengths. Allwelds are X-rayed and coated before spooling onto the reel ship.

At the time the reel ship arrives, approximately 12.5 miles of pipe isready for spooling. Thirty-nine 1,700 foot lengths of pipe are spooledaboard, stopping only to weld, X-ray and coat joints at the end of eachnew length.

The reel ship, now loaded with pipe and necessary anodes, mobilizes tolocation.

Once at location, the ship is dynamically positioned next to the firstplatform and a cable tied to the platform is attached to the pipe.

The lay operation now commences.

Anodes are added at the stern of the ship during laying. The ship isnormally stopped for 3-5 minutes to add each anode as required.

At the end of the 12.5 mile lay, the pipe is secured in a clamp at thestern of the ship. An abandonment head is welded on and the pipe loweredto the seabed with a winch. The lowering/pick up cable is attached to abuoy.

The ship then returns to the yard to spool up the second load of pipe.

Upon returning to the laydown point, the pipe is picked up and againclamped. The new pipe is welded-on, the joint is X-rayed and coated, andthe lay operation commences again. At the second platform the pipe ispulled in and secured at the platform. The pipeline is then tested andthe reel ship is demobilized.

Additional features of the reel ship and its operation are described ina paper co-authored by Kenneth R. Friman, Stanley T. Uyeda and HermanBidstrup, entitled "First Reel Pipelay Ship UnderConstruction--Applications Up to 16-inch Diameter Pipe 3000 Feet ofWater" (OTC Paper No. 3069) to be presented at the Offshore TechnologyConference in Houston, Texas, May 8-11, 1978 and contained in theproceedings thereof. Said Friman et al paper is incorporated herein inits entirely by reference thereto.

8. Summary

It will be seen from the foregoing description that the reel ship ofthis invention represents a new and different advance in the art ofoffshore reel type pipelaying techniques. In particular, the shiprepresents a new type of vessel construction which is advantageouslysuited for carrying large pipe spooling reels to conduct subseapipelaying operations quickly and economically for a world market.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The embodimentdescribed above is therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the hereafter appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

What is claimed is:
 1. A reel pipelaying vessel, comprising:a hullcomposed of a plurality of longitudinal port and starboard side primarystructural members; port and starboard side reel support structuresextending upwardly from said port and starboard side primary vesselstructural members in the midship section thereof to increase thesection modulus of the vessel in the midship section; a pipe-carryingreel; bearing means mounting the reel for rotation about a substantiallyhorizontal axis across the vessel's beam; and bearing support meansmounting the bearing means to the respective reel support structures anddistributing the load of the reel downwardly and longitudinallyoutwardly through said reel support structures and primary shipstructural members to maintain the stress on the vessel's primarystructural members within the maximum allowable stress limits for thematerials used in the construction of the vessel's primary structuralmembers; wherein the distance (in feet) from the center of gravity ofthe vessel to its transverse metacenter is no greater than about0.00194B², where B is the beam (in feet) of the vessel; and wherein theGMT of the vessel lies within the shaded portion of the graph shown inFIG. 17 of the drawing,where GMT represents the vertical distance (infeet) from the center of gravity to the transverse metacenter of thevessel, and BEAM represents the beam or width of the vessel (in feet).2. A reel pipelaying vessel, comprising:port and starboard side reelsupport structures located at a substantially midship portion of thevessel and extending to a height sufficient to accommodate the largestpermitted reel dismeter, based on maximum pipe diameter and length to becarried by the vessel; a pipe-carrying reel rotatably mounted to saidreel support structure about a substantially horizontal rotational axisextending transversely across said vessel, said reel having a shaft, apair of flanges spaces from each other and extending radially outwardfrom the shaft, and a hub coaxial with the shaft and disposed betweenthe flanges and containing at least one ballast compartment; and, meanscoupled to said reel for supplying ballast into said at least oneballast compartment in the hub; wherein the distance (in feet) from thecenter of gravity of the vessel to its transverse metacenter (GMT) is nogreater than about 0.00194B², where B is the beam (in feet) of thevessel; and wherein the GMT of the vessel lies within the shaded portionof the graph shown in FIG. 17 of the drawing, where GMT represents thevertical distance (in feet) from the center of gravity to the transversemetacenter of the vessel, and BEAM represents the beam or width of thevessel (in feet).
 3. A reel pipelaying vessel according to claim 1 or 2,wherein the ratio of vessel beam to vessel draft is in the range ofabout 2.25:1 to 4.00:1.
 4. A reel pipelaying vessel according to claim3, wherein said ratio is in the range of about 3.5:1 to 4.0:1.
 5. A reelpipelaying vessel according to claim 3, wherein each of said reelsupport structures has a substantially box-beam configuration.
 6. A reelpipelaying vessel according to claim 5, wherein the length of each ofsaid reel support structures is at least about 0.4 L, where L is thelength of the vessel.
 7. A reel pipelaying vessel according to claim 5,further comprising pipe handling means located aft of the reel forconditioning pipe as it is unspooled from the reel and for guiding theconditioned pipe into the water during a pipelaying operation.
 8. A reelpipelaying vessel, comprising:a hull composed of a plurality oflongitudinal port and starboard side primary structural members; apipe-carrying reel; port and starboard side reel support structures,each having a substantially box-beam cross-section extending upwardlyfrom said port and starboard side primary vessel structural members andabove a main deck level of the vessel in the midship section thereof toincrease the section modulus of the vessel in the midship section, saidreel support structures extending upwardly to a height sufficient toaccommodate the largest permitted reel diameter, based on maximum pipediameter and length to be carried by the vessel; and reel mounting meansfor mounting the reel to the respective reel support structures fordistributing the load of the reel downwardly and longitudinallyoutwardly through said reel support structures and primary vesselstructural members to maintain the stress on the vessel's primarystructural members within the maximum allowable stress limits for thematerials used in the construction of the vessel's primary structuralmembers.
 9. A reel pipelaying vessel according to claim 8, furthercomprising: ballasting means for adding ballast to the vessel at alocation on the vessel which approximates the effect on the vessel ofthe mass of the pipe spooled on the reel, said ballasting means beingadapted to add ballast to the vessel as pipe is unspooled to minimizechanges in the GMT of the vessel due to offloading of pipe therefrom.10. A reel pipelaying vessel according to claim 8 or 9, wherein thedistance (in feet) from the center of gravity of the vessel to itstransverse metacenter (GMT) is no greater than about 0.00194B², where Bis the beam (in feet) of the vessel.
 11. A reel pipelaying vesselaccording to claim 10, wherein the GMT of the vessel lies within theshaded portion of the graph shown in FIG. 17 of the drawing, where GMTrepresents the vertical distance (in feet) from the center of gravity tothe transverse metacenter of the vessel, BEAM represents the beam orwidth of the vessel (in feet), and T_(n) represents the natural vesselperiod (in seconds).
 12. A reel pipelaying vessel according to claim 11,wherein the GMT of the vessel is maintained between about 3' and about8' for all significant offshore operating conditions.
 13. A reelpipelaying vessel according to claim 10, wherein the length of each reelsupport structure is at least 0.4 L but less than 1.0 L, where L is thelength of the vessel.
 14. A reel pipelaying vessel according to claim10, wherein said reel support structures are further characterizedby:port and starboard side outer substantially longitudinal hull membersand port and starboard side inner longitudinal bulkheads, each extendingsubstantially the length of the ship, said hull members and bulkheadsextending vertically between a baseline level and the main deck level ofthe vessel in the forward and stern sections thereof and, in the midshipsection, from the baseline level to a height substantially above themain deck level; port and starboard side substantially horizontaltransverse midship structural members extending between the top portionsof the raised midship sections of said outer hull members and innerlongitudinal bulkheads; and at least one port and starboard sideintermediate substantially horizontal transverse member extendingbetween said outer hull members and inner longitudinal bulkheads, andspaced from the midship structural members now lower than to about themain deck level; wherein the midship portions of the outer hull membersand inner longitudinal bulkheads, the transverse midship structuralmembers, and the intermediate transverse members together comprise saidsupport structures.
 15. A reel pipelaying vessel according to claim 9,saidreel having a shaft, a pair of flanges spaced from each other andextending radially outward from the shaft, and a hub coaxial with theshaft and disposed between the flanges and including at least oneballast compartment; said ballasting means being coupled to said reelfor supplying ballast into said at least one ballast compartment in thehub and for venting the interior of the ballast compartment as ballastis supplied thereto.
 16. A reel pipelaying vessel according to claim 9or 15, wherein said ballasting means is adapted to add ballast insufficient amount to maintain the GMT of the vessel within about 30% ofits initial height between full reel and empty reel conditions.
 17. Areel pipelaying vessel according to claim 16, wherein the distance (infeet) from the center of gravity of the vessel to its transversemetacenter (GMT) is no greater than about 0.00194B², where B is the beam(in feet) of the vessel.
 18. A reel pipelaying vessel according to claim17, wherein the GMT of the vessel lies within the shaded portion of thegraph shown in FIG. 17 of the drawing, where GMT represents the verticaldistance (in feet) from the center of gravity of the transversemetacenter of the vessel, BEAM represents the beam or width of thevessel (in feet), and T_(n) represents the natural vessel period (inseconds).
 19. A reel pipelaying vessel according to claim 18, whereinthe GMT of the vessel is maintained between about 3' and about 8' forall significant offshore operating conditions.
 20. A reel pipelayingvessel according to claim 15, wherein the reel ballast meanscomprises:fill and drain conduit means coupled to one axial end of saidreel shaft through a swivel joint; first internal conduit meansextending from the first swivel joint through said shaft and into theinterior of said reel hub to provide a path for fluid ballast betweenthe interior of the hub and ballast supply and drain means; and secondinterior conduit means coupled to the second swivel joint and extendingthrough the shaft into the interior of the reel hub to provide a pathfor air to be vented from the interior of the hub to the ambientatmosphere.
 21. A reel pipelaying vessel according to claim 20, furthercomprising means for opening the vent conduit to the ambient atmosphereonly during a minor part of one complete revolution of the reel.
 22. Areel pipelaying vessel according to claim 21, wherein said vent conduitopenings comprises a cammed surface coupled for rotation with the reelshaft and switch means engageable with the cammed surface forcontrolling the operation of vent conduit valves and permitting theopening of said valves only at predetermined times.
 23. A reelpipelaying vessel according to claim 22, wherein said first and secondinterior means are disposed approximately 180° apart and wherein saidswitch means and cammed means permit opening of the vent conduit valvesonly when the second interior conduit is within about ±30° of its apexof rotation.
 24. A reel pipelaying vessel according to claim 10, furthercomprising a skeg located on the underside of the stern section of thevessel and so sized to contribute between about 1.4% and 2.1% of thevessel's buoyancy at low draft and between about 1.0% and 1.5% of thevessel's buoyancy at high draft.
 25. A reel pipelaying vessel accordingto claim 24, further having drive propellers mounted to drive shaftsextending through the hull bottom; wherein the ratio of the diameter ofthe propellers to the distance from the main water line to the center ofthe prop is in the range of from about 0.625:1 to 1.125:1 between highand low draft conditions, respectively.
 26. A reel pipelaying vesselaccording to claim 25, wherein the propellers are spaced from the hullbottom such that a distance "a" between the hull bottom and the tip ofthe propeller blades is not less than 0.2 D.
 27. A reel pipelayingvessel according to claim 26, wherein the distance "a" is preferablybetween about 0.2 D-0.4 D.
 28. A reel pipelaying vessel according toclaim 27, wherein the distance "a" is about 0.21 D.
 29. A reelpipelaying vessel according to claim 10, further comprising pipehandling means mounted to the vessel aft of the reel for conditioningpipe as it is unspooled from the reel and for guiding the conditionedpipe into the water during a pipelaying operation.
 30. A reel pipelayingvessel according to claim 16, further comprising pipe handling meansmounted to the vessel aft of the reel for conditioning pipe as it isunspooled from the reel and for guiding the conditioned pipe into thewater during a pipelaying operation.